The overall objective of this project is to design and prepare compounds that are selective for one of the forms of cyclic nucleotide phosphodiesterase from coronary arteries and to examine the potencies of these compounds as inhibitors of phosphodiesterase activites of rabbit atria and other tissue systems. We will also attempt to prepare compounds in the xanthine series that will irreversibly inhibit one of the forms of phosphodiesterase in order to develop the potential tools to investigate the relative importance of some of the multiple forms of phosphodiesterase in the physiological control of cyclic nucleotide levels.